Project Summary/Abstract Dizziness is a debilitating and common presenting symptom that prompts substantial use of diagnostic health services (i.e., tests and physician consults). The clinical utility of currently available strategies for evaluating dizziness is unknown, leading to substantial practice variation. This study aims to characterize current patterns of use of tests and specialist consults (i.e. diagnostic strategies) and to determine which strategies lead to outcomes that indicate diagnostic value. The proposed research will be carried out with the OptumLabs Data Warehouse (OLDW). OLDW is a large administrative database newly available to researchers that contains claims for over 100 million commercially insured adults of working age (18-64 years old) and Medicare Advantage members (? 65 years old) from across the U.S. Specifically, Aim 1 is to characterize variation in diagnostic strategies used for evaluations of dizziness. The variety of diagnostic strategies currently used by providers will be characterized by the choice, timing, and intensity of use of a.) diagnostic tests (audiometric, vestibular, neuroimaging, cardiac tests) and, b.) specialist consults (otolaryngology, neurology, cardiology). Patient- and provider-related factors associated with specific diagnostic strategies will be identified, and total spending on each strategy will be estimated. Aim 2 is to evaluate the impact of diagnostic strategies for dizziness on indicators of diagnostic value. Diagnostic strategies have value, according to rigorous evidence framework, when there is evidence that they improve: a) diagnostic thinking; b) therapeutic actions; c) patient outcomes; and, d) societal costs and benefits. The effects of various diagnostic strategies on outcomes that reflect each value indicator will be assessed: a) subsequent diagnostic refinement; b) initiation of treatment; c) fall-related injuries; and d) subsequent healthcare utilization for dizziness. This work represents a multidisciplinary health services research approach to identifying effective and efficient diagnostic strategies for dizziness. The proposed work will delineate the scope and consequences of variation in the way providers approach dizziness evaluations and will identify key features of diagnostic strategies that optimize diagnostic value for specific groups of patients and providers. These findings will lay the groundwork for future comparative effectiveness trials and the development of best-practice protocols that translate evidence into recommendations for clinical care for dizziness.